fix(escuchar,reproductor): add the section-heading token and screen 1-3 polish

Audit S7 plus the open items on screens 1-3. Escuchar gains the
prototype's own 52px "now listening" eyebrow header (t4:53), which is
structurally different from the 56px title row every other root uses
(t4:325) -- the earlier wiring test asserted PluriRootHeader on all five
roots, an over-broad premise now corrected to guard what actually holds:
no AppBar, and the sleep-timer action still reachable.

lib/l10n/app_en.arb

@@ -358,6 +358,7 @@
   "yourStationsTitle": "Your stations",
   "seeAllAction": "See all",
   "openFullPlayerTooltip": "Open full player",
+  "nowListeningLabel": "Now listening",
   "nothingPlayingTitle": "Nothing playing yet",
   "nothingPlayingSubtitle": "Pick a station from Your stations or search to start.",
   "nearYou": "Near you",
@@ -375,6 +376,7 @@
   "exploreTrendingSubtitle": "Today",
   "exploreNewTitle": "New",
   "exploreNewSubtitle": "This week",
+  "popularNowTitle": "Popular now",
   "offlineBannerTitle": "No connection",
   "retryAction": "Retry",
   "noStationsAvailable": "No stations available",